Self-checkout (SCO) machines provide a mechanism for customers to process their own purchases from a retailer. They are an alternative to the traditional cashier-staffed checkout. In practice, the customer assumes the job of the cashier by scanning and applying payment for the items themselves.
When a customer pays at a self-checkout machine using cash, the self-checkout machine must accept the cash and in most cases, provide change in the form of cash. In order to provide this functionality, some self-checkout machines have large amounts of stored cash for providing change and a separate capacity for receiving cash payment. Some self-checkout machines can provide multiple denominations as change from a single storage compartment but sorting through the multiple denominations to provide correct change can introduce significant delay into the transaction.